The present invention relates to a seat belt anchor attachment structure provided on an automobile pillar structure.
Conventionally used seat belts for automobiles have one end attached through an anchor to an upper portion of a side pillar structure of the automobile body and the other end extending through a retracting device to a floor member. The pillar structure is of a closed cross-section comprised of inner and outer panels which are welded together. Inside of the pillar structure, there is attached a nut plate having a nut secured thereto and the seat belt anchor is attached to the nut plate. The inner and outer panels are made of sheets of suitable metallic material which have relatively low rigidity, so that they are usually reinforced at the portion where the nut plate is to be installed. For this purpose, a stiffener is conventionally attached to the inner and outer panels of the pillar structure.
Japanese utility model publication No. 54-25768 discloses a nut plate which has a base attached at its inner side with a nut and a pair of side pieces provided along the opposite side edges of the base. The side pieces are generally perpendicular to the base and extend in the direction of the side where the nut is attached, so as to form a generally channel-shaped cross-section. The side pieces extend vertically upwards and downwards beyond the confines of the base and is welded to the side walls of the pillar outer panel. The structure as proposed by this utility model shows a high rigidity against the force perpendicular to the base due to the existence of the side pieces. However, the base has a relatively low buckling resistance and therefore the structure shows a relatively low strength against forces parallel to the base.